(1) Field of the Invention
The present invention relates to a thrust bearing and a bearing device which receive an axial force of a crankshaft of an internal combustion engine.
(2) Description of Related Art
The crankshaft of an internal combustion engine is rotatably supported at a cylinder block lower portion of the internal combustion engine via a main bearing, which is configured by combining a pair of half bearings into a cylindrical shape, at a journal portion of the crankshaft.
One or both of the pair of half bearings is used in combination with a half thrust bearing(s) which receives the axial force of the crankshaft. The half thrust bearing(s) is placed on one or both of end surfaces of the half bearing in the axial direction.
The half thrust bearing receives the axial force which occurs at the crankshaft. That is to say, the half thrust bearing is disposed for the purpose of supporting the axial force which is inputted to the crankshaft at the time that the crankshaft and the transmission are connected with each other by a clutch or the like.
In vicinities of circumferential ends of the half thrust bearing, thrust reliefs are formed on a slide surface side of the half thrust bearing so that the thickness of a bearing member becomes thinner toward circumferential end surfaces. In general, the thrust relief is formed so that its length from the circumferential end surface of the half thrust bearing to the slide surface and the depth at the circumferential end surface are formed to be constant irrespective of the position in the radial direction. The thrust relief is formed for absorbing positional displacement of the abutted end surfaces of the pair of half thrust bearings at the time of assembling the half thrust bearings into a split type bearing housing (see FIG. 10 in JP-A-H11-201145).
The crankshaft of an internal combustion engine is supported by the cylinder block lower portion of the internal combustion engine via a main bearing, which consists of a pair of half bearings, at a journal portion of the crankshaft. At this time, a lubricating oil is fed from an oil gallery in a cylinder block wall into a lubricating oil groove, which is formed along an inner circumferential surface of the main bearing, through a through-hole in a wall of the main bearing. The lubricating oil is supplied into the lubricating oil groove of the main bearing in this manner, and thereafter, is supplied to the half thrust bearing.
Meanwhile, in recent years, oil pumps for supplying the lubricating oil of internal combustion engines have been downsized, and therefore, the amount of the lubricating oil supplied to bearings has also decreased. Accordingly, the leakage amount of the lubricating oil from the end surfaces of the main bearing becomes decreased, and the supply amount of the lubricating oil to the half thrust bearing also tends to decrease. As the countermeasures against it, there has been provided the art of enhancing oil retainability for the lubricating oil by forming a plurality of fine grooves side by side on a slide surface of a half thrust bearing, for example (see JP-A-2001-323928). Further, it has been proposed to form an inclined surface (thrust relief) on the slide surface of the half thrust bearing from an end portion of the half thrust bearing in the circumferential direction to a substantially half of the height of a top portion, and thereby make the inclination angle of the inclined surface with respect to the slide surface gentle (see JP-A-2013-238277).